1. Field of the Invention
The present invention relates to a reinforcing fiber material used for reinforcing a concrete structure by sticking same on the concrete structure and impregnating the fiber with a resin, particularly a reinforcing fiber sheet prepared by arranging carbon fiber on a substrate sheet in one direction, and a concrete structure having a reinforcing layer of a fiber-reinforced composite material using such a reinforcing fiber sheet on the surface thereof.
2. Prior Art
It is conventionally the usual practice to reinforce or repair a concrete structure, such as a pier of a bridge for automobiles or railway, or a beam or a column of a building, with a fiber-reinforced composite material.
Conventional reinforcement has usually been to use a fiber-reinforced composite material prepared by sticking a prepreg to the surface of a concrete structure and curing the prepreg.
However, the prepreg has had troublesome storage so as not to cause curing, and difficulties in execution including difficult cutting into desired size and shape at the reinforcing site.
The present applicant developed therefore a reinforcing fiber sheet as a reinforcing material permitting reinforcement with a fiber-reinforced composite material by easily applying onto the surface of a concrete structure without the need for troublesome storage as in a prepreg, and proposed the reinforcing fiber sheet and a method of reinforcement with the use thereof (Japanese Patent Application Laid Open Nos. 3-222,734, 3-224,901, etc.).
The proposed reinforcing fiber sheet as described above comprises reinforcing fibers arranged, for example, in one orientation through an adhesive layer on a substrate sheet, and is to reinforce a concrete structure by sticking the reinforcing sheet onto the surface of a portion to be reinforced of the concrete structure, and curing a resin impregnated into the fiber before or after sticking to convert the reinforcing fiber sheet into a fiber-reinforced composite material.
According to this reinforcing fiber sheet, excellent effects are available, including absence of storage problems as in a prepreg, simple handling at a reinforcing site, and easy execution on the surface of a concrete structure.
Since a reinforcing bar arranged in a concrete structure yields with a strain of only about 0.15 to 0.20%, in the case where the concrete structure is continuously loaded it is necessary to reinforce the concrete structure within the range of this strain in the reinforcing bar.
For this purpose, it is the conventional practice to use a carbon fiber sheet having a modulus of elasticity of the 23.5 ton/mm.sup.2 class and a reinforcing weight of about 200 g/m.sup.2 in reinforcement with the use of a unidirectional carbon fiber sheet (a reinforcing fiber sheet having carbon fibers arranged in one direction). This carbon fiber sheet has such a low toughness per layer that it is necessary to laminate multiple layers of carbon fiber sheets on the portion to be reinforced in order to achieve reinforcement within the range of strain of from about 0.15 to 0.20%, thus resulting in a longer period for construction and a higher construction cost.